But that hasn't been enough, as Leap Wireless is set to have $100 million worth of unsold iPhones in its inventory by the summer, according to the Wall Street Journal.

In addition to being on pace to sell just half of the amount of iPhones it committed to sell in its first year, the CDMA carrier has another two years to go on its three-year contract with Apple.

With the iPhone 5S and iPhone 6 reportedly around the corner, Leap Wireless may have a lot of expensive, older-generation iPhones that it cannot sell.

No-contract iPhone 5 pitfalls

Leap Wireless' off-contract iPhone 5 plan with unlimited talk, text, and data for just $55 a month does come with some upfront sticker shock - the phone costs $500.

That's the first problem for Cricket, the nation's seventh largest carrier, which is trying to appeal to customers who want to avoid the credit checks that AT&T, Verizon and Sprint perform on new customers.

Adding to its problems, Cricket Wireless' iPhone web page reveals that the phone is not available in all areas of the country.

With tough competition from pre-paid rival Virgin Mobile, which now sells an iPhone 4 and iPhone 4S, Cricket Wireless has yet to say how it'll right its ship with just 5.3 million subscribers.